Patent application FR06/05512, filed by the applicant company on 21 Jun. 2006, discloses a nacelle for an aircraft engine comprising a cascade-type thrust reverser defining a nozzle of variable cross section.
A nacelle such as this is depicted schematically in the attached FIGS. 1 to 3.
It notably comprises a thrust reverser 1 delimiting a cold air flow path 3 with an inner structure 5 surrounding an aircraft engine (not depicted). The direction in which the air flows through this flow path is indicated by the arrow F1.
More specifically, the thrust reverser 1 comprises an outer wall 1a, able to move axially under the action of a first series of actuators 7, and an inner wall 1b able to move under the action of a second series of actuators (which are not depicted).
By operating only the first series of actuators 7 it is possible to modify the cross section of the rear part 9 of the outer wall 1a of the thrust reverser, which will then define a cold air ejection nozzle of variable cross section.
FIG. 1 depicts the outer wall 1a in the minimum cross section nozzle configuration, in which configuration the upstream zone 11 (in relation to the direction F1) of the outer wall 1a of the thrust reverser 1 slides between a cowl 13 surrounding the fan casing 21 and an annular wall 17 attached to the front frame 19 of the thrust reverser, itself attached to the fan casing 21 of the engine (it being recalled here that the front frame 19 supports cascades of vanes 23 allowing the thrust reversal function to be implemented).
FIG. 2 indicates (arrow F2) the sliding movement with which the cowl 13 may be endowed for operations of maintenance on the casing 21.
FIG. 3 indicates (arrow F3) the sliding movement with which both the outer wall 1a and the inner wall 1b may be endowed in the thrust reversal configuration, causing cold air to circulate from the flow path 3 to the outside through the thrust reversal cascades of vanes 23 (arrow F4).
One of the problems associated with the nacelle that has the aforementioned architecture relates to the interface between the outer wall 1a of the thrust reverser 1 and the cowl 13.
Specifically, for aerodynamic performance reasons, it is essential for the step 25 formed by the cowl 13 in relation to the outer wall 1a to be as shallow as possible.
It is therefore necessary that, in this zone of mutual overlap, on the one hand the thickness of the cowl 13 and on the other hand the clearance between this cowl and the outer wall 1a be minimized.
The requirement of minimal thickness for the cowl 13 prevents the provision of reinforcements (ribs or the like) for this cowl in said zone of overlap.
What this means is that this cowl 13 is liable to experience deformation in this zone, which deformation may lead to a jamming of the relative movement of the outer wall 1a in relation to the cowl 13, given the small clearances there are between these two members.